The control and mechanism of secretion of ACTH, endorphin, gamma-lipotropin, alpha MSH, CLIP, and 16K fragment will be studied using a mouse pituitary tumor cell line (AtT-20/D-16v) and primary suspensions and cultures of rat anterior and intermediate pituitary cells. Cells will be incubated in medium containing radioactive amino acids to label the hormone pools in the cells. Established immunochemical procedures will be used to isolate radiolabeled molecules secreted in response to secretagogues and in the presence of agents which block secretion. The electrophysiological events which accompany these changes in secretory rate will be monitored by intracellular recordings. Thus, the secretion of different peptide regions of the 30K common precursor will be investigated in cells from several different tissues.